Circuit boards (e.g., motherboards) often contain single in-line package (SIP) modules such as circuit boards, electrical devices, resistors, capacitors, or other electronic equipment. The SIP modules include connectors, fingers, leads, contacts, pins, or other interface members arranged in a single line on an edge of the board. Typically, the connectors or fingers are included on both sides of the board. The modules are mounted to the motherboard in a perpendicular fashion to maximize the number of devices, components, circuit boards, or equipment attached to the motherboard.
In general, SIP modules or other circuit boards are manufactured by etching a copper layer or layers on an insulated substrate to form a conductive pattern including trace lines and contact pads (e.g., footprints, finger connectors, or other features) for electrical devices or interconnection systems. The trace lines electrically connect the contact pads to various other contact pads on the circuit board. SIP modules or other circuit boards typically include contact pads such as finger connectors which serve as interfaces between the motherboard or other circuit board and the module. The finger connectors or other connecting features are typically located proximate the edge of the module and allow the module to physically and electrically engage the motherboard.
After the module is etched, a solder mask is applied to the board. The solder mask is applied to the circuit board in a photo-imaged solder mask pattern. The solder mask pattern prevents solder in subsequent manufacturing steps from attaching to portions of the board covered by the solder mask pattern. The solder mask pattern is generally applied in a photo-sensitive process in which the solder mask is screened on or curtain coated to cover the entire circuit board and exposed to light (e.g., infrared light) through a reverse-imaged photographic film artwork arranged according to the solder mask pattern. This solder mask is cured to the board in the solder mask pattern after exposure to light through the photographic film artwork. After curing, the solder mask cannot be easily removed from the board without deforming or otherwise destroying portions of the circuit board. Examples of such solder mask or solder resist are Probimer 52 M.TM. manufactured by Cyba-Giegy, 8200.TM. manufactured by Dexter-Hysol, two-part epoxy solder resist, or other types of solder resist.
After the solder mask is cured in the solder mask pattern, unwanted solder mask covering conductive areas that accept electrical components (e.g., solder mask outside the solder mask pattern) is taken off by plunging the board in an aqueous bath of solder mask remover, thereby leaving the solder mask pattern on the board. After the solder mask pattern is applied to the board, electrical devices are placed on the various contact pads, features or connection areas on the board. The board is exposed to a solder wave to physically and electrically attach (e.g., solder) the electrical devices to the board. Alternatively, the devices can be soldered to the board by infrared (IR) reflow soldering or vapor phase soldering. After the electrical devices are soldered to the board, the board or module is attached to the motherboard or other circuit board.
The fingers or other connecting features are utilized to physically and/or electrically interface the motherboard to the module. Module interconnection systems (e.g., connectors, header assemblies, connection features such as those described in U.S. patent application Ser. No. 08/316,667 which is the parent of this application, slot edge connectors, card connectors, printed circuit (PC) board connectors, or other hardware) physically engage the fingers to support the module at a 90.degree. angle with respect to the board. For example, the edge of a module such as a video card including finger connectors can be inserted into a slot edge connector on the motherboard of a personal computer. The module is held in the slot edge connector by a friction fit between the edge of the video card and the slot edge connector. Alternatively, the edge of a module can be inserted through a hole in the motherboard, and the fingers of the module can be soldered to other fingers on the motherboard by a wave soldering technique as described in U.S. patent application Ser. No. 08/316,667.
Fingers or other connecting features for interfacing boards together are generally made from metal conductors such as tin lead solder (PbSn), palladium nickel (PdNi), gold plate (Au), an organic coating (e.g., ENTEK.TM.), electroless NiAu over Cu, Bismuth (Bi) over Cu, or other conductive material. The finger connectors typically must be manually taped with polyamide film tape or high temperature covering to prevent the solder from the solder wave or other soldering technique utilized to attach the electrical devices to the module from accumulating on the finger connectors. If solder attaches to the finger connectors, the finger connectors cannot properly engage, interference fit, or otherwise interface with the interconnection system on the motherboard. Additionally, if the solder wave touches finger connectors made of gold plate, the gold from the finger connectors can mix into the solder bath and spoil the entire solder bath associated with the solder wave. After soldering, the tape must be manually removed before the module is attached to the motherboard. Such manual taping steps are expensive, time consuming and add to the cost of assembling the module or other circuit board.
Heretofore, solder mask has not been applied to the finger connectors to prevent the solder from attaching to the finger connectors because the solder mask becomes essentially permanently attached to the fingers, thereby preventing a suitable physical and electrical engagement with the interconnection system. Thus, there is a need for contact areas or finger connectors for a motherboard, SIP module, or other circuit board which do not need to be manually taped. Further, there is a need for a solder mask pattern which can be removably applied to the finger connectors and yet prevent solder from attaching to the finger connectors. Further still, there is a need for a solder masking technique for the finger connectors which is low cost, does not add extra manufacturing steps, allows the module to be efficiently connected to the motherboard, reliably protects the finger connectors, and utilizes conventional solder mask materials.